Optical networks are progressively sending data signals at higher transmission rates and over longer distances. However, certain limitations affecting the signal integrity of the optical transmissions have begun to emerge. One such limitation is polarization mode dispersion (PMD).
An optical beam may travel in multiple polarization modes through a light transmission guide. For example, an optical beam may have a transverse magnetic (TM) polarization mode and an orthogonal transverse electrical (TE) polarization mode. Although these polarization modes naturally travel at the same speed, certain conditions could cause one of the modes to travel faster than the other resulting in PMD. PMD may result from slight irregularities in the structure of the fiber as well as mechanical stress upon the fiber caused by, for example, bending, vibrations, and thermal cycling. Because of the mechanical and structural sensitivity of the optical pulses sent through stretches of fiber, PMD has been proven difficult to compensate for. The effects of PMD will become more pronounced as optical networks proceed from 10 Gb/s to 40 Gb/s and beyond.